Inexpensive organic solar cell and method of producing same

ABSTRACT

Inexpensive organic solar cell and method of producing same The present invention proposes an organic photovoltaic component, particularly an organic solar cell, whose electrode is implemented as unstructured and is provided with a passivation layer, so that the passivated electrode layer acts functionally as a structured electrode or electrode layer.

The present invention concerns the field of organic semiconductorcomponents. In particular, the present invention concerns the field ofphotovoltaics, including photovoltaics based on organic components.

Photovoltaics, particularly in the form of the so-called solar cell,provides a noise-free and emission-free method of producing electricalenergy. For many years, a stumbling block to the broad dissemination ofphotovoltaic systems for generating electricity has been their highproduction cost, particularly in the case of so-called first-generationphotovoltaic systems. First-generation photovoltaic systems or solarcells are based on crystalline silicon wafers, which are complex andtherefore expensive to manufacture and process. Typical first-generationphotovoltaic systems reached efficiencies of about 15%. The secondgeneration, so-called thin-film solar cells, use semiconductor layers afew microns thick and are therefore cheaper to manufacture than thefirst-generation cells. However, second-generation photovoltaic systemshave yet to match the efficiency of the first generation, insteadexhibiting efficiencies in the 3% to 7% range.

In addition to production cost and efficiency, the mechanical propertiesof photovoltaic systems are of interest in opening up as many fields ofapplication as possible for their use. The first- and second-generationsystems have to be mounted on a substantially mechanically rigidsubstrate, usually glass. The third-generation systems currently indevelopment address this problem. The third-generation systems are verylow-weight and can be mounted on a mechanically flexible substrate, thusopening up new and promising fields of application. Polymer films, inparticular, are used as substrates in these systems. Another factor thatmay help to minimize the production cost of the third-generation systemswould be for them to become competitive in terms of output and energycost with the power supplies now in use.

The heretofore-known production methods for solar cells and solar cellmodules, particularly organic solar cells and solar cell modules, aresubject to numerous constraints that lead to onerous and cost-intensivemethods of fabrication, as well as fundamental physical andcircuitry-related disadvantages.

Indium/tin oxide (ITO) electrodes have typically been used heretofore,and also serve as the substrate in organic solar cells. Indium/tin oxide(ITO) electrodes are expensive, and their electrical conductivity is lowin comparison to other standard conductors such as metallic conductors,for example, a fact that can be a disadvantage particularly in therealization of large-area organic solar cells; and the processing ofindium/tin oxide (ITO) electrodes, particularly their structuring, canbe done only by means of wet chemical etching processes.

One object of the present invention is, therefore, to provide analternative to the customary structuring of the electrodes that both isinexpensive to perform and affords a multiplicity of choices for thematerial of the electrode. Inexpensive substrates are of particularinterest.

A further object of the present invention is to increase the electricalconductivity of the electrodes so that alternative materials of lowerelectrical conductivity can be used.

A further object of the present invention is additionally to enable theelectrodes to be structured in such a way that both parallel and seriesinterconnection of individual organic solar cell modules is feasible.

The object of the invention is achieved by means of the inventivesubject matter defined by a passivated electrode or electrode layer inclaim 1 and claim 13.

Provided according to the invention is an organic photovoltaiccomponent, particularly an organic solar cell, whose electrode isimplemented as unstructured and is provided with a passivation layer insuch a way that the result, functionally, is a structured electrode.

The passivation layer is preferably selectively implemented. Inparticular, the selective passivation layer can cover the electroderegionally and/or have varying layer thicknesses. The passivation layeradvantageously has a layer thickness in a range of 100 nm to a few tensof microns. The passivation layer is preferably a dielectric.

According to one embodiment, the electrode is provided with additionalconduction paths to increase the electrical conductivity of theelectrode. The conduction paths are advantageously also covered by thepassivation layer.

According to a further embodiment, the electrode simultaneously servesas the substrate.

According to a further embodiment, individual regions of thephotovoltaic component, particularly of the organic solar cell, areinterconnected in circuit in an edge region. This interconnection isadvantageously done in series or in parallel. The individual regions arepreferably produced by mechanical structuring.

According to the invention, a method is provided for producing anorganic photovoltaic component, particularly an organic solar cell. Tobegin with, an unstructured electrode layer is provided. Next, apassivation layer is deposited on the unstructured electrode layer toproduce a passivated electrode layer that substantially corresponds inits functional nature to a structured electrode layer.

Details and preferred embodiments of the inventive subject matter willemerge from the dependent claims and the drawings, with reference towhich exemplary embodiments are explained in detail below to make theinventive subject matter clearly apparent. In the drawings:

FIG. 1 is a sectional view of an unstructured electrode layer (bottomelectrode) applied to a substrate, according to one embodiment of theinvention;

FIG. 2, in continuation of FIG. 1, additionally shows conduction landsapplied to the electrode according to the embodiment of the invention;

FIG. 3, in continuation of FIG. 2, shows selectively passivated regionsof the unstructured electrode and the conduction lands by means ofpassivation [sic] according to the embodiment of the invention;

FIG. 4, in continuation of FIG. 3, shows a semiconductor layer appliedin structured form according to the embodiment of the invention; and

FIG. 5, in continuation of FIG. 4, shows an electrode layer (topelectrode) applied in structured form according to the embodiment of theinvention.

FIGS. 1 to 5 show, by way of example, the sequence of steps involved inlayer application during the production process of an organic solar cellserving as an exemplary embodiment of the present invention.

Organic components, particularly organic semiconductor components, aregenerally defined by the fact that at least one functional unit is atleast partly organic in nature. With reference to organic semiconductorcomponents, it is to be understood correlatively that one at least one[sic] of the functional layers, such as, for example, the substrate,bottom electrode layer, semiconductor layer, top electrode layer,through contacts, conduction path elements, etc., is composed at leastpredominantly of an organic material. Candidate organic materials,particularly polymeric materials, will be identified in the course ofthe following detailed description of the embodiments of the invention.It should be understood, however, that the present invention is notlimited to the organic materials and any inorganic materials listedbelow.

The term “organic materials” should be understood to mean any types oforganic, metalorganic and/or inorganic synthetic materials with theexception of classic semiconductor materials based on germanium,silicon, and so on. Further, the term “organic material” also is notintended to be limited to carbon-containing material, but rather,materials such as silicone are also possibilities. Furthermore, inaddition to polymeric and oligomeric materials, “small molecules” canlikewise be used.

Turning now to FIG. 1, applied to a substrate 1 is a first electrodelayer, which will be referred to hereinafter as the bottom electrodelayer.

The substrate 1, which serves as a carrier for the organic solar celldescribed as an exemplary embodiment, is preferably formed of a flexiblematerial, i.e. a mechanically flexible material. For example, thin glassplates and polymer films can be considered for this purpose. In the areaof polymer or synthetic films, for example polyethylene terephthalate,polyimide and polyester films are also used. The thickness of thesubstrate basically determines the overall thickness of the component,since the layer thickness or layer heights of the functional layersapplied to substrate 1 are orders of magnitude smaller. The thickness ofsubstrate 1 is typically in the range of 0.05 to 0.5 mm. The substratethickness can naturally be above or below the foregoing range, dependingon the area of application. Specifically, the use of large substratethicknesses is advisable in cases where the organic components, circuitsor systems in question must be resistant to mechanical stress.

The bottom electrode layer 2 is applied unstructured to substrate 1. Theelectrode layer can be made from a wide variety of materials, i.e., bothorganic and metallic materials can be contemplated, depending on thechoice of production process and the demands placed on the electrodelayer. One might particularly mention in this connection indium/tinoxide (ITO), doped polyethylene (PEDOT), polyaniline (PANI), silver(Ag), gold (Au) and other inert metals, organic semiconductors,nanoparticulate solutions (for example indium/tin oxide (ITO)nanoparticles, zinc oxide (ZnO) nanoparticles, etc. This list should notbe considered definitive.

Conventionally, to make an organic solar cell it is necessary tostructure the bottom electrode layer 2 so that the organic solar cellcan function. This structuring is done by selectively ablating thebottom electrode layer 2 in predefined regions. Structuring of this kindis typically done by wet chemical etching, which is a cumbersome processthat usually requires handling highly reactive and environmentallyundesirable chemicals.

The concept of the present invention provides for no structuring of thebottom electrode layer. Instead of structuring the bottom electrode,i.e. ablating the conductive material from the areas where it is notwanted, it is proposed according to the invention to passivate theconductive material. The term “passivation” as used herein is understoodto mean that an additive insulating layer is applied to the electrodelayer, i.e. in this case bottom electrode layer 2, thus resulting inmasking with respect to the layer next applied to the bottom electrodelayer. The passivation is done selectively, i.e., in/on predefinedregions of the electrode layer and with individually tailored layerthicknesses for each of the predefined regions masked by a passivationlayer. The passivation layer is advantageously applied from solution,particularly by low-cost printing or coating methods. The layerthickness of the passivation layer can be adjusted individually and canrange, for example, from a few 100 nm (nanometers) to as much as a fewtens of microns (μm).

One functionally critical factor is the electrically insulating propertyof the passivation layer with respect to an electrically conductivelayer applied thereto, i.e. an electrode layer, for example a topelectrode layer. A suitable dielectric is therefore used as the materialof the passivation layer. The dielectric can, for example, be inorganicor organic, and thus polymeric, in nature.

The inventively proposed passivation has still further advantages overthe conventionally provided structured electrode layer.

Non-planarities, unevennesses in the electrode layer that might causeshort circuits, can also be deliberately masked. This makes it possible,in an improvement, to apply to the electrode layer electricallyconductive lands, as well as more complexly structured conductorarrangements, such as lattice-shaped conductor arrangements, forexample, made of highly conductive material, as illustrated in FIG. 2 bythe example of two conduction lands 3 a and 3 b. Structures of thiskind, composed of conduction lands applied to an electrode layer,sharply improve the overall conductivity of the electrode layer, herebottom electrode layer 2. These conductive lands, which can have layerheights ranging from a few tens of nanometers to a few or more microns,can be either vapor-deposited, i.e. by physical gas phase deposition of,for example, silver (Ag) or copper (Cu), or printed on, i.e. by meansof, for example, a screen printing process employing silver (Ag) screenprinting paste.

Since these paths are subsequently passivated by means of an insulatinglater, i.e. the passivation layer, they can be produced in a largelyarbitrary height or layer thickness, for example in a range of a fewtens of nanometers to a few tens of microns.

Illustrated by way of example in FIG. 4 is the selectively passivatedbottom electrode layer 2 with conduction lands 3 a and 3 b. In keepingwith its selectivity, the structured passivation layer arranged onbottom electrode layer 2 is composed of individual passivationstructures or passivation regions 4 a to 4 d, which are disposed inindividual regions on the bottom electrode layer and each have their ownlayer thicknesses or layer heights. Conduction lands 3 a and 3 b withpassivation structures 4 b and 4 c have smaller layer thicknesses thanpassivation structures 4 a and 4 d, which in this case are intended, byway of example, for the provision or production of contacts (see FIG. 5and the following description).

Care should be taken to ensure that the edges or the configuration of aprinted passivation layer do not lead to the separation, due to themushroom effect, of an electrode layer disposed above the passivationlayer, such as, for example, the top electrode layer.

To summarize, it can be noted ab initio that the inventively proposedunstructured electrode layer with selective passivation is thefunctional equivalent of a structured electrode layer. The productionprocess for such an unstructured electrode layer with selectivepassivation is advantageous over the production process for a structuredelectrode layer. The selective passivation also has additionaladvantages, particularly both those described in the foregoing and thosedescribed below.

Referring to FIG. 4, a semiconductor layer 5 at least partially coveringbottom electrode layer 2 will now be described. Semiconductor layer 5also covers passivated conduction lands 3 a and 3 b. This means that thetotal layer height of conduction lands 3 a, 3 b and the passivationlayer applied thereto (passivation structures 4 b and 4 c) isimplemented in this case, by way of example, in such a way that thistotal layer height is smaller than the layer thickness of semiconductorlayer 5. As a result, conduction lands 3 a and 3 b with their associatedpassivation layers are completely embedded in semiconductor layer 5.

Exemplarily illustrated semiconductor layer 5 covers in particular aregion of bottom electrode layer 2 that is bounded by passivationstructures 4 a and 4 d of the passivation layer applied to bottomelectrode layer 2.

Semiconductor layer 5 can be implemented as either an inorganic or,preferably, an organic semiconductor layer. Known organic semiconductorlayers are composed, for example, of polythiophenes, polyalkylthiophene,polydihexylterthiophene (PDHTT), polythienylene vinylenes, polyfluorenederivatives, or conjugated polymers, merely to mention a non-limitingselection of candidate organic materials. The semiconductor layer 5 cantypically be processed from solution by spin coating, doctor blading orprinting.

FIG. 5, finally, shows the organic solar cell according to the inventiveembodiment with, covering semiconductor layer 5, an electrode layer thatwill be designated hereinafter as top electrode 6 owing to itsarrangement relative to substrate 1. The electrode layer can be made ofan extremely wide variety of materials, i.e. both organic and metallicmaterials can be contemplated, depending on the choice of productionprocess and the demands placed on the electrode layer. For the sake ofcompleteness, the foregoing examples may be consulted for candidateexemplary materials listed with reference to the bottom electrode layer.

Top electrode layer 6 is implemented in the illustrated exemplaryembodiment in such a way that passivation structure 4 a of thepassivation layer, which is not covered by semiconductor layer 5, is atleast partially covered by top electrode layer 6. Contrastingly,passivation structure 4 d of the passivation layer, which also is notcovered by semiconductor layer 5, is not covered by top electrode layer6 as well. By means of passivation structure 4 d, which is suitable foruse as an isolating element with respect to top electrode layer 6 in theplane of that layer, a contact 20 can be realized that is connected tobottom electrode layer 2 and is insulated with respect to the topelectrode layer. A vertical contact element to bottom electrode layer 2can be made, for example, from the electrically conductive material ofwhich top electrode layer 6 is composed. Such a vertical contact elementfor contact 20 can be produced simultaneously with the application oftop electrode layer 6.

A corresponding contact 10 that connects to top electrode layer 6 isadvantageously realized in a region of top electrode layer 6 in whichtop electrode layer 6 covers passivation structure 4 a. As describedabove, passivation structure 4 a isolates electrode layers 2 and 6 fromeach other electrically.

With reference to multi-part, modular organic photovoltaiccomponents/organic solar cells, based on the inventive concept astructuring of the electrodes that is advantageously easy to produce canbe chosen for the module wiring.

To obtain individual active regions on substrate 1 that can beinterconnected in series, it is necessary to divide bottom electrodelayer 2. With parallel interconnection, such division is not necessary.Division of this kind is conventionally performed by wet lithographicprocesses. In connection with the proposed inventive concept, thedivision of the electrode layer can advantageously be effected bymechanical structuring. Two processes in particular are suitable forthis mechanical structuring: (i) laser structuring and (ii) mechanicalscribing or cutting. Since these divided regions are subsequentlyrepassivated by the passivation layer (dielectric) and any edges will becovered, no special care or precision need be devoted to the quality ofthe division.

In contrast to inorganic solar cells, which are conventionally coupledto modules in series by Z-connection, further according to the inventionan advantageously simpler wiring scheme is proposed that, in particular,places fewer demands on precision of production. In the production oforganic solar cells by means of coating processes, the edge region canbe kept free of printed layers without any difficulty. Only slight (orvery slight) demands are placed on printing resolution in such cases.The interconnection can be done in this edge region during theapplication of the top electrode layer, which is, for example, depositedor printed from the gas phase. Since the remaining electrode regions arepassivated by the dielectric, only slight (or minimal) demands need beplaced on precision.

The following embodiments can be realized by means of theabove-described passivation of bottom electrode layer 2.

The first embodiment of an organic solar cell is illustrated in detailin FIG. 5. This embodiment of the organic solar cell comprisesadditional conduction lands, illustrated by way of example in the formof conduction lands 3 a and 3 b, which are also passivated, i.e.,covered with the applied passivation layer.

A second implementation of an organic solar cell is essentially the sameas the embodiment depicted in FIG. 5. This embodiment of the organicsolar cell is provided with a passivated bottom electrode layer but hasno additional conduction lands, i.e., the conduction lands illustratedby way of example in FIG. 5 in the form of conduction lands 3 a and 3 bare not present in this embodiment.

A third implementation of an organic solar cell also comprises apassivated bottom electrode layer, which can be provided either with orwithout passivated conduction lands. The individual elements of theorganic solar cell are connected in parallel. The bottom electrode layercan therefore be implemented over a broad area or implemented instructured form, divided into individual regions. The individual regionscan be formed by the above-described mechanical structuring method.

A fourth embodiment of an organic solar cell again provides a passivatedbottom electrode layer that also can be provided either with or withoutpassivated conduction lands. The individual elements of the organicsolar cell are preferably connected in series in this case. The bottomelectrode layer is consequently divided into individual regions over abroad area. The individual regions can be formed by the above-describedmechanical structuring method.

A fifth embodiment of an organic solar cell essentially provides one ofthe above-described embodiments, in which the interconnection in circuitof the individual elements takes place in the non-printed edge region ofthe elements.

In the context of a sixth embodiment of an organic solar cell, proposedaccording to invention is a metallic substrate 1 that has electricalconduction properties and can therefore simultaneously serve as a bottomelectrode layer. Said metallic substrate 1 can, for example, be a metalfoil, a steel sheet, a film provided with a thin metal layer, etc. Thefilm, particularly an organic film such as a polymer film, for example,could be provided with the thin metal layer for example by vapordeposition of copper (Cu), for example. Such metallized films are known,for example, in the field of flexible printed circuit boards.

1. An organic photovoltaic component, having an electrode layer that isunstructured and includes a passivation layer, the electrode andpassivation layer forming a passivated electrode layer that functionallycorresponds to a structured electrode.
 2. The organic photovoltaiccomponent as recited in claim 1, wherein said passivation layer isselectively implemented.
 3. The organic photovoltaic component asrecited in claim 2, wherein the selective passivation layer regionallymasks the electrode.
 4. The organic photovoltaic component as recitedclaim 2, wherein said selective passivation layer has varying layerthicknesses.
 5. The organic photovoltaic component as recited in claim1, wherein said passivation layer can have a layer thickness in a rangeof 100 nm to a few tens of microns.
 6. The organic photovoltaiccomponent as recited in claim 1, wherein said passivation layer is adielectric.
 7. The organic photovoltaic component as recited in claim 1,wherein the electrode can be provided with additional conduction pathsto increase the electrical conductivity of said electrode.
 8. Theorganic photovoltaic component as recited in claim 5, wherein saidconduction paths are also covered by said passivation layer.
 9. Theorganic photovoltaic component as recited in claim 1, wherein saidelectrode simultaneously serves as the substrate.
 10. The organicphotovoltaic component as recited in claim 1, wherein individual regionsof said photovoltaic component are interconnected in circuit, saidinterconnection in circuit being effected in an edge region.
 11. Theorganic photovoltaic component as recited in claim 10, wherein saidinterconnection in circuit can be done in series or in parallel.
 12. Theorganic photovoltaic component as recited in claim 10, wherein theindividual regions are produced by mechanical structuring.
 13. A methodof fabricating an organic photovoltaic component, the method comprising:providing an unstructured electrode layer; and depositing a passivationlayer on said unstructured electrode layer to yield what is functionallya structured electrode layer.
 14. An organic photovoltaic component,comprising: An unstructured electrode layer; and a passivation layer onthe electrode layer so that the components is in the form of astructured electrode.